In recent years, hermetic compressors used in electric refrigerator-freezers desirably have increased efficiency for less power consumption, reduced noise, and increased reliability.
There is a conventional hermetic compressor of this type which includes a ball bearing as a thrust bearing to increase efficiency (see, for example, Patent Literature 1).
The conventional hermetic compressor will be described as follows with reference to the drawings.
FIG. 4 is a longitudinal sectional view of the conventional hermetic compressor. FIG. 5 is an exploded perspective view of an essential part of the conventional hermetic compressor.
In FIG. 4 and FIG. 5, lubricating oil 4 is stored in the bottom of hermetic container 2. Hermetic container 2 includes compressor body 6 resiliently supported by suspension springs (not illustrated).
Compressor body 6 includes motor element 10 and compression element 12 disposed above motor element 10. Motor element 10 includes stator 14 and rotor 16.
Compressor element 12 includes shaft 19 which includes main shaft 20, arm 21 disposed at the upper end of main shaft 20, and eccentric shaft 22 extending from the top surface of arm 21. Main shaft 20, to which rotor 16 is fixed, is rotatably supported by main bearing 26 of cylinder block 24. A compression load applied to eccentric shaft 22 is supported by main shaft 20 and main bearing 26 which are disposed below eccentric shaft 22 so as to form a cantilever bearing.
Shaft 19 has lubrication mechanism 29 including inclined hole 27 inside main shaft 20, lead groove 28 on the surface of main shaft 20, and the like.
Piston 30 is reciprocatable in cylinder 34 having a substantially cylindrical inner surface in cylinder block 24. Connection portion 36 has ends each provided with a hole. Piston pin 38 of piston 30 and eccentric shaft 22 are fitted into the holes so as to connect eccentric shaft 22 and piston 30.
Cylinder 34 and piston 30 form compression space 42 together with valve plate 40 disposed on the open end face of cylinder 34. Valve plate 40 is covered with fixed cylinder head 44.
Cylinder head 44 is equipped with intake muffler 46 which is molded with a resin such as PBT (polybutylene terephthalate) and which has a sound absorbing space inside.
The following is a description of thrust ball bearing 50.
Main bearing 26 includes, on the upper end surface, thrust face 52 which is a planar portion perpendicular to the central axis.
Thrust ball bearing 50, which includes upper race 54, steel balls 56 held by holder 58, and lower race 60, is disposed above thrust face 52.
Upper race 54 and lower race 60 are annular metal plates each having parallel top and bottom sides. Holder 58 is annular in shape and has a plurality of holes in the circumferential direction in which steel balls 56 are held rotatably.
On thrust face 52, lower race 60, steel balls 56 held by holder 58, and upper race 54 are stacked in contact with each other in this order. Arm 21 of shaft 19 is placed on the top surface of upper race 54.
The hermetic compressor having the above-described structure operates as follows.
When electric power is supplied to motor element 10, stator 14 generates a rotating magnetic field, which allows rotor 16 to rotate with main shaft 20. The rotation of main shaft 20 causes eccentric motion of eccentric shaft 22, which is transmitted to piston 30 via connection portion 36, allowing piston 30 to reciprocate in cylinder 34.
A refrigerant returned from a refrigeration cycle (not illustrated) outside hermetic container 2 is introduced into compression space 42 via intake muffler 46, compressed by piston 30 in compression space 42, and sent from hermetic container 2 to the refrigeration cycle.
The bottom of shaft 19 is soaked in lubricating oil 4, so that the rotation of shaft 19 allows lubricating oil 4 to be supplied by lubrication mechanism 29 to each unit of compression element 12 so as to lubricate the sliding part.
Thrust ball bearing 50 is a rolling bearing in which steel balls 56 are made to roll while being in point contact with upper race 54 and lower race 60. Thrust ball bearing 50 is rotatable while supporting a vertical axial load such as the weights of shaft 19 and rotor 16. Rolling bearings have less friction than generally-used thrust ball bearings which are slide bearings, and thus, a force to be applied can be reduced, leading to increased efficiency.
In the above conventional structure, however, use of a thrust ball bearing in an inverter compressor involving high-speed rotation at a frequency greater than a power-supply frequency results in an unstable contact between the steel balls and the upper and lower races in the thrust ball bearing at high-speed rotation at a frequency greater than the power-supply frequency. The unstable contact is caused because the upper and lower races generally have minute unevenness on the surfaces. Such unstable contact leads to increased noise and vibration.